As depicted in FIGS. 1A-1C, in conventional turbocharged locomotive two-stroke diesel engine systems 101 having an air/exhaust system 103, the turbocharger 100 draws air from the atmosphere 116, which is filtered using a conventional air filter 118. The filtered air is compressed by a compressor 102. The compressor 102 is powered by a turbine 104, as will be discussed in further detail below. A larger portion of the compressed air (or “charge air”) is transferred to an aftercooler (or otherwise referred to as a heat exchanger, charge air cooler, or intercooler) 120 where the charge air is cooled to a select temperature. Another smaller portion of the compressed air is transferred to a crankcase ventilation oil separator 122, which evacuates the crankcase 114 in the engine; entrains crankcase gas; and filters entrained crankcase oil before releasing the mixture of crankcase gas and compressed air into the atmosphere 116.
As best seen in FIG. 1A, the cooled charge air from the aftercooler 120 enters the engine 106 via an airbox 108. The decrease in charge air intake temperature provides a denser intake charge to the engine, which reduces NOX emissions while improving fuel economy. The airbox 108 is a single enclosure, which distributes the cooled air to a power assembly 110 including a plurality of cylinders 125 arranged in two banks 127a, 127b. Each of the cylinders 125 is closed by a cylinder head 126. As best seen in FIG. 1B, fuel injectors 121 in the cylinder heads 126 introduce fuel into each of the cylinders 125 where the fuel is mixed and combusted with the cooled charge air. Each cylinder 125 includes a piston 128 which transfers the resultant force from combustion to the crankshaft 130 via a connecting rod 132. Each piston 128 includes a piston bowl, which facilitates mixture of fuel and trapped gas (including cooled charge air) necessary for combustion. The cylinder heads 126 include exhaust ports controlled by exhaust valves 134 mounted in the cylinder heads 126, which regulate the amount of exhaust gases expelled from the cylinders 125 after combustion.
The combustion cycle of a diesel engine includes, what is referred to as, scavenging and mixing processes. During the scavenging and mixing processes, a positive pressure gradient is maintained from the intake port of the airbox 108 to the exhaust manifold 112 such that the cooled charge air from the airbox 108 charges the cylinders and scavenges most of the combusted gas from the previous combustion cycle. More specifically, during the scavenging process in the power assembly 110, the cooled charge air enters one end of a cylinder 125 through intake port 135 controlled by an associated piston 128. (see FIG. 1B). The cooled charge air mixes with a small amount of combusted gas remaining from the previous cycle. At the same time, the larger amount of combusted gas exits the other end of the cylinder via four exhaust valves and enters the exhaust manifold 112 along paths 136 as exhaust gas. The control of these scavenging and mixing processes is instrumental in emissions reduction, as well as in achieving desired levels of fuel economy.
Exhaust gases from the combustion cycle exit the engine 106 via an exhaust manifold 112. The exhaust gas flow from the engine 106 is used to power the turbine 104 and thereby power the compressor 102 of the turbocharger 100. After powering the turbine 104, the exhaust gases are released into the atmosphere 116 via an exhaust stack 124 or silencer.
The exhaust gases released into the atmosphere by internal combustion engines such as the locomotive diesel engine system in FIGS. 1A-1C include particulates, nitrogen oxides (NOX) and other pollutants such as hydrocarbon and carbon monoxide. Legislation has been passed to reduce the amount of pollutants that may be released into the atmosphere. Traditional systems have been implemented which reduce these pollutants, but at the expense of fuel efficiency.
Emissions reduction systems have previously been employed to reduce NOx and particulate matter (PM), hydrocarbon (HC), and/or carbon monoxide (CO) emissions in a series flow arrangement. That is, the exhaust gas stream first passes through a NOX emission reduction unit and then a filtration unit for PM/HC/CO reduction (or vice versa). In such systems, the emissions reduction equipment also is applied to the exhaust gas from all cylinders of the engine collectively. As a result, the backpressure of the turbine 104 generally increases, thereby causing the pressure to drop at the system components. Because the system components are installed in series, the total pressure drop is the summation of the pressure drop of each of these components.
Because of the increase in backpressure, the expansion of gases in the cylinder and at the turbine is reduced, which causes a reduction in the power level obtained from the cylinder and turbine 104 and affects the scavenging and mixing processes in a two-stroke engine. Also, the turbine 104 cannot deliver enough power to the compressor 102, which reduces the turbocharger 100 speed and the amount of air supplied to engine 106. As a result, the amount of fuel that may be burned effectively in the cylinders is reduced, causing further power reduction of the engine 106. Therefore, when the conventional exhaust emission reduction equipment is added to the engine 106, engine power is reduced; engine fuel consumption is increased; and, scavenging and mixing desired in the two-stroke engine is affected. Therefore, there is a need for an airflow system that reduces PM/HC/CO and NOx emissions without significantly increasing backpressure.
The various embodiments of the presently disclosed system may be able to exceed one or more of what is referred in the industry as, the Environmental Protection Agency's (EPA) Tier II (40 CFR 92), Tier III (40 CFR 1033), and Tier IV (40 CFR 1033) emission requirements, as well as the European Commission (EURO) Tier Mb emission requirements.
Locomotives must also be able to operate within specific length, width, and height constraints. For example, the length of the locomotive must be below that which is necessary for it to negotiate track curvatures or a minimum track radius. In another example, the width and height of the locomotive must be below that which is necessary for it to clear tunnels or overhead obstructions. Locomotives have been designed to utilize all space available within these size constraints. Therefore, locomotives have limited space available for adding new system components thereon. Accordingly, there is a need to provide a system for reducing emissions and backpressure, the components of which may integrated within the limited size constraints of the locomotive and preferably within the same general framework of an existing locomotive. There is still further a need for a system for reducing emissions and backpressure, which system may operate in a locomotive operating environment.